Assembly Language data?

Hello, I am doing PC to PC communication using C programming.
I want to know the meaning of this data
in.h.ah=00;
in.h.al=0x0a7?
what is 0x0a7?
why is the 0x before 0a7.
If we write 0x01 then what is it? is it 01h?
Why cant we only write it as 01h?